The invention relates generally to microwave heating apparatus and more particularly to waveguide applicators for heating or drying products with microwaves.
Microwaves are often used in industrial processes to heat or dry products. For example, U.S. Pat. No. 4,497,759 describes a waveguide system for dielectrically heating a crystalline polymer drawn into a rod fed continuously through a circular waveguide applicator along its centerline. The TM01 mode is used to concentrate the heating along the centerline. The narrow waveguide applicator has an inner diameter of 95.6 mm, which limits its use to small-diameter products, such as drawn polymer rods. For continuous heating and drying processes in which individual products or a product strand is fed continuously through a waveguide applicator, openings are provided at opposite ends of the applicator for product entry and exit. But microwave radiation can also leak through the openings, especially if the openings are large to accommodate large-diameter products.